The present invention relates broadly to intrusion security devices, and in particular to a bistatic pulse-overlap Doppler radar for intrusion detection.
In the prior art, electronic detection devices utilizing the Doppler principle have been widely used for some years. Such devices detect a change in received frequency from the transmitted frequency, the difference being the Doppler shift. Whether the frequency shift is positive or negative, it is detected by the detection device after processing by using an integrator, the output of which reaches an alarm threshold level after a period of time which is determined by the energy level that is transferred to the integrator input. While such devices should ignore spurious signals that may be generated by external environmental influences which alter the nature of the received signal, they do not always do so thus resulting in the generation of false alarms.
In the case of frequency discriminating devices of the above type, the detector may not be able to discern between small oscillatory noise or vibration sources and real signals. Sources of this type cause phase jitter on the received signal and can fall within the pass-band of the receiver and which when combined with the appropriate mean phase of the received signal, can cause false alarms. While real signals produce either a positive or negative Doppler shift that are caused by a moving body within the field of the detection devices, false returns that appear to be real signals are accepted by the detection device.